I noticed this super ko rule a while back and decided to add a unit
test to my program to ensure it complies. In designing my test I
tried to find the shortest possible game that had a superko. Here is
what I came up with:
a2 b1 b2 c2 b3 d1 a3 a1 c1
Now the move b1 is illegal on KGS under Chinese rules (although legal
under all other KGS rule variants).

That's right. Chinese rules use the simpler positional superko,
while AGA and NZ use situational superko, which also takes turn into
account.